A Broker Example: Three Syntaxes - One Semantics

Relfun is exemplified here by a simple broker program that
decides which products to buy for customers.
Relfun's classical Prolog-like and Lisp-like syntaxes are
augmented by the recent XML-based RFML syntax.
It is important to notice that all three syntaxes stand for
one semantics (enabling, e.g., a Lisp-XML-Prolog-Lisp round trip):